The present invention relates to an on-site installation type differential pressure or pressure indicating transmitter (to be generally referred to as a differential pressure/pressure transmitter hereinafter) to be used in various types of plates such as petrochemical, chemical, power, gas, food, and steel plants and, more particularly, to a differential pressure/pressure transmitter that can change the attaching angle and direction with respect to process fluid supply pipelines, the reading direction of the indicator (meter), and the like freely in accordance with the situation of the installation site.
In general, a differential pressure/pressure transmitter to be installed on site is constituted by a detecting section (pressure-receiving section) which detects the differential pressure of a to-be-measured fluid applied to a pair of barrier diaphragms, and a transmitting section (converting section) which has a power supply connecting terminal block and output monitoring indicator and transmits a differential pressure signal detected by the detecting section to an internal indicator or an external device such as a controller or recorder.
The positions of the detecting and transmitting sections are determined in accordance with the piping state of the process fluid supply pipelines on site, the surrounding atmosphere of the installation side, and the like. More specifically, different piping states on site, surrounding atmospheres, and the like are coped with by separately changing the position of the detecting section itself, the connecting state of a transmitting section housing to the detecting section, the attaching angle of the indicator, the attaching position and direction of a terminal block, to which electrical wires are to be connected, with respect to the transmitting section housing, and the like.
Regarding the installation conditions of the transmitter, for example, whether the process fluid supply pipelines are arranged vertically or horizontally, on which side the high-pressure pipeline and low-pressure pipeline are located, in which direction the indicator is to be recognized visually when the pipelines are arranged along a wall, and the like change depending on sites. Hence, the positions of the indicator and terminal block with respect to the process fluid supply pipelines must be changed in accordance with these installation conditions.
Therefore, in a conventional differential pressure/pressure transmitter of this type, as described in Japanese Utility Model Laid-Open No. 61-112248 (reference 1) and Japanese Patent Laid-Open No. 4-291126 (reference 2), the housing of a transmitting section to which electrical wiring lines are to be connected is rotatably attached to the body of a detecting section which detects the differential pressure of a process fluid. A meter case is attached to the housing of the transmitting section such that its angle can be changed, and a meter is built into the meter case such that its angle can be changed in the circumferential direction. Alternatively, the type of the housing may be changed (to a product individually matching the pipelines) because it is limited by the shapes of the pressure introducing covers which are to be attached to the side surfaces of the detecting section to introduce pressure to the barrier diaphragms, or the shape of a fixing metal fixture for fixing the transmitting section to the detecting section may be changed (a special adapter is used), to cope with different installation site conditions.
The differential pressure/pressure transmitter described in reference 1 comprises a transmitter case constituted by a first cylindrical case for accommodating an amplifier unit and indicator, and a second cylindrical case for accommodating a terminal block. The second cylindrical case which has a pair of wiring line connection ports formed in its lower and side portions is connected to an obliquely lower portion of the first cylindrical case to be integral with it. The first cylindrical case is attached to the detecting section such that its attaching angle can be adjusted. The indicator is built into the first cylindrical case such that its attaching angle can be adjusted.
The differential pressure/pressure transmitter described in reference 2 comprises a detector body, a transmitting section housing to be pivotally attached to the extending end of the detector body, and a meter housing pivotally attached to a connection opening formed in the transmitting section housing. The meter is built into the meter housing such that its posture can be changed among a plurality of attaching angular positions.
In this manner, according to the differential pressure/pressure transmitters described in references 1 and 2, the posture and direction of the transmitting section and indicator with respect to the detecting section can be changed independently of each other in accordance with the piping state of the process fluid supply pipelines at the installation site.
As described above, the conventional on-site-type differential pressure/pressure transmitter is formed such that the posture and reading direction of the transmitting section housing and meter can be changed freely in accordance with the situation of the installation site. However, the attaching angle, direction, and the like of the detecting section itself cannot be changed. More specifically, according to the conventional differential pressure/pressure transmitter described above, the pair of pressure introducing covers that cover two side surfaces of the detecting section are usually fixed to a support column through brackets, and pipeline connection flanges are fixed to the upper surfaces of the respective covers. The flanges and process fluid supply pipelines are connected to each other through pipes. The process fluid from the pipelines is guided to the pressure introducing holes of the respective covers through the pipes and flanges.
Therefore, if the detecting section is to be rotated through 90° within a vertical plane so that the facing direction of the transmitting section housing may be changed from forward to upward or vice versa, it cannot be changed because the transmitting section housing abuts against the pipelines or flanges.
If the detecting section is installed sideways to have a vertical axis so that the barrier diaphragms are horizontal, when a drain stays on the surface of the barrier diaphragm that is located at an upper position, the diaphragm itself deforms due to the weight of the drain to cause a measurement error. For this reason, the detecting section must be installed such that its axis is horizontal regardless of whether the pipelines are horizontal or vertical, that is, such that the barrier diaphragms are always vertical. Accordingly, depending on the directions of the pipelines, limitations may be posed that the attaching directions of the pressure introducing covers cannot be changed.
Regarding the pair of pressure introducing covers, they are usually attached to the pipelines or support column with two bolts for each cover usually, i.e., with a total of four bolts. According to the conventional product standard, however, the pitches of bolts that are adjacent vertically and horizontally are not all equal, but four bolts form a rectangle. Therefore, installation of the detecting section must differ between a case wherein the process fluid supply pipelines are arranged horizontally and a case wherein they are arranged vertically. More specifically, in horizontal installation in which the differential pressure/pressure transmitter is to be installed for a pipe body that is usually arranged horizontally, the pair of covers are fixed to oppose each other in the axial directions of the pipe body so that the transmitting section faces forward.
In vertical installation in which the differential pressure/pressure transmitter is to be installed for a pipe body that is arranged vertically, as the barrier diaphragms must be vertical, the pair of covers must be fixed to oppose each other in a direction perpendicular to the axial direction of the pipe body. In this case, however, the covers are fixed as they are rotated through 90° with respect to the pipe body, and accordingly the positions of the bolts are inevitably shifted by 90°. Since the pressure introducing holes of the pressure introducing covers and the pressure extracting ports of the pipe body are also shifted from each other by 90°, the covers cannot be actually attached. For this reason, two different transmitters, i.e., one for vertical installation and one for horizontal installation, must be designed, or a special adapter must be used.
If the shapes of the pressure introducing covers are changed in accordance with the shapes of the pipelines or a special adapter is used, the number of types of the covers or adapters increases, so that alteration after shipping cannot be made. If spare covers and adapters are not prepared, demands from clients cannot be met.